This invention relates to controlling the solution viscosity and other rheological properties of associative thickeners in aqueous media. More particularly, this invention relates to aqueous formulations of hydrophobically modified polyacetal-polyethers (HM-PAPEs) and cyclodextrins to suppress and control the solution viscosity of such thickeners. This invention also relates to the use of these associative thickener formulations in systems that are to be thickened such as water-borne paints.
Highly filled aqueous systems, such as water-borne coatings (latex or emulsion paints), inks, construction materials, and cosmetics are formulated with hydrophobically modified water-soluble polymers (HM-WSPs) to control the rheology of coatings during manufacturing, storage and applications. These HM-WSPs are commonly referred to in the art as xe2x80x9cassociative thickenersxe2x80x9d. They are so called because they thicken the latex paints by forming a three-dimensional network through intermolecular associations of the hydrophobic moieties present in the HM-WSP chains and/or with other hydrophobic components present in the coatings formulation. Water-borne architectural coatings are used for on-site application to interior or exterior surfaces of residential, commercial, institutional, or industrial buildings. Associative thickeners have become the industry standards as the rheology modifiers in paints because they have a number of advantages over conventional thickener systems. These include: (1) a lower viscosity during incorporation, (2) a lower tendency to spatter during application, (3) good flow and leveling upon application, (4) better color, (5) higher gloss through less flocculation, (6) lower sensitivity of the coatings to water, (7) less vulnerability to microbial degradation, and (8) minimal reduction in the viscosity of the thickened dispersions on exposure to shearing (approaching Newtonian flow behavior).
These associative thickeners are normally sold as high solids solutions in water or a mixture of water and an organic cosolvent, such as butyl carbitol or propylene glycol. The function of these cosolvents is to suppress the viscosity of the aqueous solution containing the associative thickener to allow for ease of handling before it is used as a thickener. While these organic cosolvents perform their intended function, they possess potential environmental, safety, and health problems. These organic cosolvents contribute to volatile organic compounds (VOCs) which are not environmentally friendly. Since these VOCs potentially harm the atmosphere, environmentalists are getting bills passed in the Government in order to reduce the VOCs emitted into the atmosphere. Hence, companies that produce or market formulations that produce large volumes of VOCs are being required either to reduce the level of VOCs or to eliminate them all together. Companies in the paint industry are now concerned about VOCs and are asking their suppliers to provide environmentally friendly products with low or no VOCs.
One approach to suppress the aqueous viscosity of associative thickeners and yet be environmentally friendly is to use surfactants in the paint. Although this presents no specific health or environmental hazard, it does degrade formulation performance. U.S. Pat. No. 6,150,445 describes the use of nonionic surfactants in small amounts, which owing to their micelle-forming capability can reduce the viscosity of the aqueous concentrate of the associative thickener.
Another approach is described in U.S. Pat. Nos. 5,137,571 and 5,376,709 that disclose the use of cyclodextrins or their derivatives to suppress the solution viscosity of hydrophobically modified ethoxylated polyurethanes, hydrophobically modified alkali-soluble emulsions, hydrophobically modified hydroxyethylcellulose, or hydrophobically modified polyacrylamides.
Another approach is to reduce the molecular weight of the associative thickener so that no viscosity suppressant is needed to prepare high solids solutions in water with manageable viscosity.
Recently, the compositions and applications of a new class of associative thickeners based on hydrophobically modified polyacetal (ketal)-polyether were described in U.S. Pat. Nos. 5,574,127 and 6,162,877. Compared to many existing associative thickeners (see U.S. Pat. No. 5,574,127), these polymers were useful as rheology modifiers for highly filled aqueous systems at very high pHs to provide the desired properties. However, like many high molecular weight associative thickeners, these polymers exhibit high viscosity at high solids solutions in water. Consequently, their use in many commercial applications is restricted.
Therefore, to widen the utility of these associative thickeners, it is desirable to develop means to lower their high solids solution viscosity. The present invention is directed to address this issue.
The present invention is directed to a composition comprising a dry blend of a) a hydrophobically modified polyacetal-polyether (HM-PAPE) or comb HM-PAPE and b) a viscosity suppressing agent selected from cyclodextrins and derivatives thereof. Optionally, this dry blend can be heated to fuse the materials together to form a solid mass.
This invention also relates to a method for improving the pumpability and pourability of aqueous solutions of HM-PAPE or comb HM-PAPE comprising admixing a cyclodextrin with the HM-PAPE or comb HM-PAPE to form a complex of the cyclodextrin and HM-PAPE or comb HM-PAPE where the viscosity of the HM-PAPE or comb HM-PAPE is suppressed and adding the complexed admixture to an aqueous system containing a water-insoluble polymer wherein the cyclodextrin is decomplexed and the HM-PAPE or comb HM-PAPE becomes an effective thickener.